In order for aircraft seating to be certified for use in an aircraft, the seat must pass a series of performance tests to ensure that it will withstand the various dynamic forces that it may be subjected to, particularly in an emergency situation. In order to be certified as airworthy, aircraft seating designs must pass a series of dynamic tests that simulate aircraft deformation and impulse during emergency conditions. The airworthiness standards for seat structures are described in Federal Aviation Regulation § 25.562, the contents of which is incorporated herein.
Because of the standards set forth in FAR § 25.562, aircraft seating must be strong enough not only support the weight of the seat occupant, but also to withstand the various load forces that are generated as a result of maneuvers performed by the pilot during flight, upon landing or, more importantly, in the event of an emergency. These various load forces are known as g-forces and result from the forces of acceleration that pull on the seat and its occupant when changes occur in the motion of the aircraft.
G-forces can be either positive or negative and can result from either an acceleration or deceleration of the aircraft. Most individuals involved in aviation are familiar with the positive g forces that result from an aircraft being pulled through a tight radius of turn. In such a turn, the force of the acceleration is increased as greater lift is required to maintain level flight in the turn. This acceleration is a function of the velocity of the aircraft and the radius of the turn and is determined by the equation:a=v2/rwhere a is the acceleration force, v is the velocity of the aircraft and r is the radius of the turn. This acceleration force a is then divided by g (32 ft/s2) to determine the number of g's resulting from the turn. The number of g's is the multiplier used to determine the weight of an object as a result of the increased acceleration. For example, under a load of 4 g's, an object weighing 10 pounds will feel as though it weighs 40 pounds.
In addition to acceleration loads encountered in a turn, g loads are also experienced during periods of rapid acceleration or deceleration such as occurs during the takeoff and landing phase of a flight. These g forces, which act laterally to the aircraft and its occupants, exert a rearward force with respect to the aircraft during periods of acceleration, thereby forcing one back into the seat on takeoff, and a forward force during the period of deceleration on landing, thereby pulling one forward in the seat.
During a normal take-off and landing evolution, a passenger absorbs this g-loading by either pressing back in the seat or leaning forward. In the event of an emergency or crash landing, however, the seat frame itself must be capable of absorbing a load of up to 16 g's without being deformed or, even worse, snapped out of the floor of the aircraft. This is particularly true of a sideways facing seat such as a divan used in general aviation and business jet type aircraft.
While a passenger absorbs the g-load by either pressing back in the seat or leaning forward, the seat frame itself must absorb the load in order to prevent it from being deformed or, even worse, snapped out of the floor of the aircraft. Conventional seats are mounted to the floor of the aircraft cabin in such a manner that there is no “give” in the seat that would allow it to absorb the dynamic forces resulting from an emergency or crash landing. Because of this, the passenger absorbs all of the dynamic forces as he is pulled forward in a seat during an emergency landing.
In a side facing divan, such as is used on a general aviation aircraft, the occupant is not pushed back into the seat on takeoff, but rather slides to their right or left depending on which side of the aircraft they are sitting. Because the seat is attached to the floor using a fixed L or T-shaped foot fitting, the seat frame is subject to greater deformation as it is unable to move to absorb the dynamic loads generated by an emergency or hard landing. For this reasons, a passenger seat that is attached to the floor of an aircraft so as to allow for some rotational freedom to help absorb the g forces while having a self-aligning capability would be an important improvement in the art.